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When air conditioner parts are being replaced on your vehicle, you may hear the term “AC system flush” come up, either as a general industry practice, or at a shop where you are getting the repair. What you need to know is that performing this function is absolutely vital, and we’ll explain why, and what you need to do the job.

What is an AC Flush?

An AC flush, in simple terms, is the act of using compressed air to send a solution through the AC system, which cleanses and grabs any contaminants and particles, and flushes them out of the system. An AC flush is only performed when the system is opened, or when a major component like the AC compressor is changed out.

While doing this may seem simple, the practice is often overlooked or skipped by DIYers, which can cause a myriad of problems if contaminants are in the system. When done properly, the evaporator, condenser, and AC lines are all properly flushed clean, while the compressor and accumulator / receiver drier are changed.

Why AC Systems Need Flushing

The AC system is a closed, self-contained system composed of 2 things – refrigerant, which is what makes the system have its cooling properties, and oil, needed to properly lubricate the system’s compressor – the only moving part. Any time the AC system is opened to the atmosphere, the probability of contaminants entering the system is high. When a component like the AC compressor fails, contaminants are often ejected into the system from the failing compressor.

Once contaminants are in the system, these will recirculate, and it’s only a matter of time before they can cause more components, like a brand-new AC compressor, to fail. When a newly installed compressor fails, the vast majority of the time it’s because of contaminants in the system.

When AC Systems Need Flushing

Anytime your AC compressor has failed and is being changed, an AC flush should always be performed. Any time the system is opened, or has been opened, a flush should be performed. If you are operating on a system that has sat idle and without refrigerant for a long period of time (like a project car), the entire system should be flushed before attempting to recharge the system. You will use a flushing tool to blast out the evaporator, condenser, and then clean each AC line. 

Once flushed, the hoses can be put back on, the compressor attached, along with a new receiver drier or accumulator. It’s important to note that any time the AC system is opened, the receiver drier or accumulator should always be changed.

How to Flush Your Car’s AC System

AutoZone carries an AC flush tool in their Loan-A-Tool program, part number 57377. This tool allows you to fill AC flush solution into the bottle, and then use compressed air to blast this solution through the AC components, flushing any debris out. AutoZone’s Loan-A-tool program also carries the vacuum pump and manifold gauges necessary to service your AC system. 

If you’re unsure about doing these functions, you can always search through our Preferred Shops for someone in your area that does AC repairs and flushes. To do a flush, you will need the following items:

To properly flush the system, follow these steps:

1

Setting Things Up

In most cases of an AC flush, the car will be parked, and the AC system opened, usually by the lines at the compressor being disconnected. Remove the receiver drier / accumulator and all AC lines leading to the evaporator and condenser.

2

Start with the Evaporator

Start by flushing the evaporator, which is the fittings leading into the firewall. Use your piece of heater hose to slip over one of the threaded fittings and feed the hose into your empty bucket.

Next, use your flushing tool to blast the flush solution into the other hose inlet. The air and flush solution will then drain out and into the bucket, along with any contaminants.

3

Next, the Condenser

Next, move to the condenser, repeating the same process by putting the hose on the lower of the two fittings on the condenser, and blasting flush solution through the condenser.

4

Then the AC Hoses

Next, take each AC hose that was removed and put one end of the hose in the bucket. Blast flush solution through the hose. Take note, if the hose has the accumulator / receiver drier attached at the point, you will want to remove it since it will be replaced with a new unit. Some hoses have a built in accumulator / drier. In these cases, the hose will need to be replaced.

5

Reattach the Hoses

Once everything has been flushed, the hoses can be reattached with new o-rings, and the compressor installed.

6

Check Your Work

At this point, the system should be brought under vacuum to check for any leaks, and to remove all atmospheric air from the system. Then, recharge the AC system using the proper amount of oil and refrigerant.

The Takeaway

Flushing the AC system of your car is not a step that should ever be skipped, especially when servicing the AC compressor. For an AC system to properly work, the system must be 100% clean of any contaminants, and be 100% refrigerant and oil only. Any deviation from this can and will cause compressor and system failure. Do the job right and do it right the first time! Stop into AutoZone today for all the tools and parts to complete your AC repair.

Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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